1. Field of the Invention
The present invention relates to solid-liquid separators, and more particularly to a new and improved device for centrifugally separating solids from liquids in a liquid/solid mixture in two distinct separation stages that occur during a single pass of the mixture through the device.
2. Description of the Prior Art
It is often desirable to separate solid particles from liquid/solid mixtures or slurries to clarify or purify the remaining liquid. When significant quantities of solids are present, it is impractical to use mesh filters since they will quickly clog and be rendered useless. As a result, centrifugal liquid-solid separators have been developed in the prior art. These devices utilize centrifugal force and gravity to achieve varying degrees of separation of solids from solid/liquid mixtures. The separated solids generally settle to the bottom of the centrifugal chamber from which they are periodically removed.
Many existing centrifugal liquid-solid separators rely upon the rotation of an internal rotor, impeller or blades to create a centrifugal action inside the chamber where the fluid is introduced. Unfortunately, the centrally located rotors in such designs take up considerable space which blocks much of the internal centrifugal flow.
Other existing separators utilize the general principles set forth in U.S. Pat. No. 4,072,481 which discloses a vortex system where the solids/liquid mixture is introduced into a cylindrical chamber at a tangential angle generating centrifugal action in the mixture. In the simple separator of U.S. Pat. No. 5,622,545, a mixture of liquids and gasses is directed in a downward helical path along the internal wall of a cylindrical chamber. A perforated separator tube is provided at the center of the cylinder for receiving gasses which flow toward the center; the gasses escape at the top, and the relatively gas-free liquid is then discharged at the bottom of the chamber. The use of a plurality of simple vortex tubes for solid-liquid-gas-oil separation is disclosed in U.S. Pat. No. 5,827,357.
The employment of a spin plate at the bottom of a vortex tube for reversing the axial direction of flow is shown in the '481 patent above, and in U.S. Pat. Nos. 5,368,735 and 5,811,006. Both of these patents additionally disclose a tube leading from a quiescent region of fluid back to the vortex for re-introduction into the flow. U.S. Pat. No. 6,090,276 discloses a similar but more elaborate re-introduction system which includes additional filtration. In each of these inventions, the separated liquid exits through a smaller tube provided at the top of the cylindrical chamber, and the solids settle at the bottom. The '006 patent also describes turbulence reducing baffles at the bottom. The invention of U.S. Pat. No. 6,143,175 discloses a vortex tube separator having an outer acceptance chamber having a plurality of tangentially oriented entrance slots through which the fluid enters the main cylinder to form the vortex.
Each of the above inventions demonstrates yet another attempt to more completely separate and remove solids from solid/liquid mixtures. However, as demonstrated by the many additional features found in later inventions, complete separation in a vortex-based centrifugal system has yet to be fully achieved.